TPS Voltage

Discussion in 'Fox 5.0 Mustang Tech' started by pearlnotchback, Dec 2, 2012.


  1. pearlnotchback

    pearlnotchback Active Member

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    Today I decided to check the voltage on my TPS because the car has been idling crappy and you have to keep your foot on the gas to keep it running on cold start up. I'm a little confused. I had the car idling and I had my voltmeter grounded and as soon as I probed the green wire on the TPS the car idled up to like 1500 and stayed there and the only way to get it to drop back down was unplug the TPS. I thought it must be a coincidence so I did it again and sure enough it jumped up to 1500 and stayed. Could the TPS be bad? What is everyones thought on this? Also something else I noticed is when I have the car idling I can just unplug the TPS and it doesnt change anything as far as how it idles or anything else and when I plug it back in the motor will surge for about half a second and continue to idle like it was. Im confused :shrug:
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  2. pearlnotchback

    pearlnotchback Active Member

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    Anyone? Anyone at all?
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  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    You put your thread in a forum specifically for people who have tuning questions about things like injectors, MAFs and aftermarket tuners such as Tweecer, Moates or Anderson PMS. Therefore you post will not been seen by people who may have an answer but do not visit the Tuner forum. Convertible top problems have nothing to do with tuning an engine.

    My advice to you is to twofold:
    1.) Send a PM to one of the moderators and have your thread moved to 5.0 Tech
    2.) Next time you start a thread, think about where it goes. If you are new to Stangnet, please read the terms of service and give extra thought to where your new thread belongs. There is some help in the text below to help you find the best place to start your thread.

    Tuning problems go in 5.0 Tuning, with specific emphasis on modifications to the injectors, MAF and computer, along with aftermarket tuners such as Tweecer, Moates or Anderson PMS.

    General tech problems go in 5.0 Tech. Tech is for suspension, electrical, brakes, body, engine repair and general troubleshooting on the computer & trouble codes

    Tall tales about your 5.0 Mustang, pictures of your 5.0 Mustang project and stories about your last trip to the race track go in 5.0 Talk.

    Do this and you'll get the best answers quicker and not get lost in the maze of posts about everything but the type of problem you are having.


    Having said that, here's some help...


    TPS problems & Troubleshooting

    Setting the TPS at .98 or .99 volt is a Bozo Internet Myth. When the computer powers up and initializes the TPS sensor, whatever it reads is the zero starting point for it. In other words your .98 volt becomes 0 volts and the computer watches for increases in voltage from that point upward.


    Setting the TPS: you'll need a good Digital Voltmeter (DVM) to do the job. Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy. Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems.


    Wire colors & functions:
    Orange/white = 5 volt VREF from the computer
    Dark Green/lt green = TPS output to computer
    Black/white = Signal ground from computer

    TPS troubleshooting steps:
    1.) Use the Orange/white & Black white wires to verify the TPS has the correct 5 volts source from the computer.
    2.) Use the Dark Green/lt green & Black/white wires to set the TPS base voltage. Try this... All you need is less than 1.0 volt at idle and more than 4.25 at Wide Open Throttle (WOT). You'll need a voltmeter with a 1 or 3 volt low scale to do the job.

    The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal) and the Black/White wire (TPS ground) to set the TPS. Use a pair of safety pins to probe the TPS connector from the rear of the connector. You may find it a little difficult to make a good connection, but keep trying. Put the safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run position but the engine isn't running. Set the voltmeter on the 2 volt range if it doesn’t auto range.

    Here’s a TPS tip I got from NoGo50

    When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks.

    (copied from MustangMax, Glendale AZ)

    A.) Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.

    B.) When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.

    C.) Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

    D.) The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

    The TPS is a variable resistor, must like the volume control knob on a cheap radio. We have all heard them crackle and pop when the volume is adjusted. The TPS sensor has the same problem: wear on the resistor element makes places that create electrical noise. This electrical noise confuses the computer, because it expects to see a smooth increase or decrease as the throttle is opened or closed.

    TPS testing: most of the time a failed TPS will set code 23 or 63, but not always. Use either an analog meter or a DVM with an analog bar graph and connect the leads as instructed above. Turn the ignition switch to the Run position, but do not start the engine. Note the voltage with the throttle closed. Slowly open the throttle and watch the voltage increase smoothly, slowly close the throttle and watch the voltage decrease smoothly. If the voltage jumps around and isn’t smooth, the TPS has some worn places in the resistor element. When the throttle is closed, make sure that the voltage is the same as what it was when you started. If it varies more than 10%, the TPS is suspect of being worn in the idle range of its travel.

    TPS will not go below 1 volt
    Engine mounted sensor circuit: Check the resistance between the black/white wire on the TPS and battery ground. It should be less than 1.5 ohms. Higher resistance than 1.5 ohms indicates a problem with the 10 pin connector, computer or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the black/white wire.

    [​IMG]

    See the graphic for the location of the 10 pin connectors:
    Diagram courtesy of Tmoss & Stang&2birds

    [​IMG]

    See the graphic for the 10 pin connector circuit layout.
    [​IMG]

    Unplug the white 10 pin connector to do some resistance testing. It is good time to clean the connector pins and examine the connector for corrosion, broken wire or other damage. See http://oldfuelinjection.com/?p=85 for help in this department.

    If the resistance on the TPS Black/White wire and pin 1 of the white engine fuel injector harness 10 pin connector, is more than 1.0 ohm, you have bad connection or broken wiring. Repeat the test using the pin 1 of the white body side 10 pin connector and battery ground. You should have less that 1.5 ohm. More than that is a damaged signal ground inside the computer or bad connections or wiring.


    Troubleshoooting idle problems
    See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. The checklist is right here in the Stangnet 5.0 Tech forum and you don’t have navigate to some other unknown web site. It‘s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

    The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.[/b]
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  4. flyinhigh90

    flyinhigh90 Member

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    im no genius but i believe u have to zero it out with the car off ..... u might want google it..... google goes along ways but my understanding by what u first posted i would try with the car off and make sure the voltage reads zero and tighten everything up and u should be good other than that your idle air control might be faulty or dirty..
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    You'll need to find a copy of the computer manual for the Mustang. Once you do, it will verify what I said. Look for eectch98.pdf and it should have the details. If you don't have a good understanding of microprocessor architecture, it probably won't mean much to you.
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  6. scoozy58

    scoozy58 Member

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    hi, i'm a dummy. i see the green and orange wires for my TPS, i am not understanding where the two probes from the DVM are going. i cannot put them into the green and orange? thankyou.
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  7. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Go back and re-read my first post: it explains everything in detail, including the functions of the wires.
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